Some years ago I thought it was, so tried to find evidence, but could not. Today on the web I can't find any evidence either; in fact, two sites say the fruit IS edible. I am discounting the article in the Daily Mail (17 August 2013) where Monty Don says "every part of the plant is poisonous".

Having said that, the leaves and the pip of the fruit are poisonous.

Do not bother eatng the fruit though; it is insipid and can be bitter.